Sampling type oscilloscope system



July 4, 1967 J. s. SHREVE SAMPLING TYPE OSCILLOSCOPE SYSTEM 2 Sheets-Sheet l Filed April 2o. 1964 FIG.

INVENTOR JAMES S. SHREVE FIG., 3

July 4, 1967 J S. SHREVE SAMPLING TYPE OSCILLOSCOPE SYSTEM Filed April 2o, 1964 2 Sheets-Sheet 2 INVENTQR JAMES s. sHR'Evr-z United States Patent O 3,329,857 SAMPLING TYPE USCILLOSCOPE SYSTEM James S. Shreve, 2055 N. Brandywine St., Arlington, Va. 22207 Filed Apr. 20, 1964, Ser. No. 361,083 s Claims. (C1. 315-18) This invention relates to a means for deflecting the electron beam of a cathode ray tube with high-frequency electrical signals.

In the past, high-frequency cathode ray tubes have employed extremely fast sweeping speeds. This has required that a high-energy electron beam be employed to produce a visible trace. In order for the input signal to produce an acceptable deection of the high-energy electron beam, the deflection plates have been made in the form of a transmission line progressing down the tube in such a manner that a given portion of the signal is in the proximity of the same portion of the electron beam for a considerable length of time, thus allowing a more progounced interaction between the signal and the electron earn.

Such devices are limited by the speed at which the beam can be swept, by the brightness of trace that can be produced at high sweep speeds, and by the duration of interaction -between the signal and the electron beam that can be attained. Increasing the beam energy to increase trace brightness reduces sweep speed and signal deiiection. In addition, there reaches a point where the voltage required to produce an energetic enough beam becomes prohibitive. X-rays, which present a hazard to personnel, are also generated by energetic beams.

Now according to the temporal sampling theorem of modern communication theory, a waveform is completely described by a series of instantaneous amplitude values spaced at a maximum interval of 1/zW seconds, where W is the upper frequency limit of the waveform sampled. To reconstruct the original waveform from the set of samples, each sample is replaced by a sin X/X function weighted by the sample amplitude. Thus, if the electron beam of an oscilloscope were made to sweep horizontally between a series of pairs of vertical deflection plates, each pair of plates having a potential difference proportional to an amplitude sample yof some desired signal, and having a configuration such that the electric lield approximates a sin X /X function, then the electron beam deection would follow the waveform of the signal. If a function other than sin X/X function is used some distortion will be introduced. In practice, a sin X/X function cannot be attained precisely; a bell-shaped function may be substituted with only slight distortion. Note that the resulting vertical deiiection of the electron beam is a function only of the horizontal deflection of the beam, and thus the horizontal sweep speed may be made as slow as desired.

It is therefore an object of the invention to provide a means for deflecting the electron beam of a cathode ray oscilloscope in a manner such that a high-energy electron beam is not required, nor is a fast sweep speed necessary, in lorder to display the waveforms of high-frequency signals on the oscilloscope screen.

It is a further object of the invention to provide a means for sampling the amplitude of a signal at a number of points simultaneously, and for storing these samples for a period of time.

It is a further object of the invention to provide a means for deiiecting the electron beam of an oscilloscope by these stored samples in such a manner that a faithful representation -of the waveform of the sampled signal is produced by the beam lon the oscilloscope screen.

These and other objects of the invention will be `apparent from the following description having reference to the accompanying drawings it being intended that the specific embodiments therein sh-own shall be taken as merely illustrative and not restrictive.

In the drawings:

FIGURE 1 is the elevation view of the deection assembly. Some of the supporting members have been omitted from this view for clarity.

FIGURE 2 is a sectional view of the deflection assembly taken along line 2 2 of FIGURE 1.

FIGURE 3 shows the deliection circuit.

FIGURE 4 is a plan view of anodes.

FIGURE 5 is the plan view of the deflection system.

Referring to FIGURE l, the deiiection assembly comprises a cathode 1 in the form of a relatively long strip, a heating element 2 which heats the cathode, anodes 3, inner conductor 4, outer conductor 5, supporting leads 6, and supporting base 7 which is an electrical insulator. The anode supporting leads 8 are shown in FIGURE 2. The anodes are adjacent but do not make electrical contact.

The above elements form a transmission line, as is indicated in FIGURE 3, when the effective deection circuit cathode and anodes are not conducting. To insure this condition of non-conduction, a negative potential is applied at each anode terminal 9 through separate large resistors 10. The center conductor of the transmission line is the inner conductor 4, while the outer conductor 5 and cathode 1 form the transmission-fine common conductor or shield. The anodes may be considered electrically floating for high-frequency signals, and thus to a first approximation the presence of the anodes does not alfect the characteristics of the transmission line.

The input signal Whose waveform is to be displayed is applied at the input terminals 11 and 12, which are connected to one end of the transmission line. A pulse generator 13 is connected to the terminals 14 and 15 at the opposite end of the transmission line. The pulse generator has an output impedance equal to the characteristic impedance of the transmission line, and thus the pulse generator serves as a termination for it, eliminating reflections from that end of the transmission line. v

Each anode 3 and the portion of the cathode 1 in proximity to the anode form an electronic diode. The pulse generator 13 is one which emits an extremely narrow positive pulse when it is triggered by an external means. This pulse travels down the transmission line in the direction opposite to that Iof the input signal. As it passes by each anode 3, it raises the electrical potential of the anode by virtue of the capacitive coupling between the inner conductor 4 and the anode 3. The amplitude of the pulse is made great enough so that electronic conduction will take place between the cathode and the anode. The amount of charge transferred by the electronic conduction is approximately proportional to the potential difference between the cathode and the anode, which is the algebraic sum of the original bias potential placed on the anode by the resistor 10, the amplitude of the pulse generated Iby the pulse generator 13, and the amplitude of the input .signal at t-he -anode under consideration at the instant the pulse passes by. Thus, after the pulse has passed by, the electric potential remaining on the anode is proportional to an instantaneous amplitude value of the input signal plus a iixed value determined by the original bias potential and the pulse amplitude. After the pulse has traversed the entire transmission line, the electric potentials remaining on the plurality of anodes constitute a sampling of the input waveform which completely determines that waveform. After considerable time, the electrical charge on each anode will drain away through the resistors 10, and the electrical potential will return to the original bias level.

Referring to FIGURE 5, the deflection assembly 16, described above, serves to vertically deflect the electron beam 17 in a cathode ray tube. The deflection assembly, along with an electron gun 18, horizontal deflection plates 19, and fluorescent screen 20, is located within the envelope 21 of the cathode ray tube. Referring to FIGURE 2, the electron beam 17 passes between each anode 3 and the inner conductor 4 in turn as it is swept horizontally. Any potential difference between an anode and the inner conductor will deflect the electron beam as it passes by.

Referring to FIGURE 4, the anodes 3 are flat plates lying in a horizontal plane. Each anode is .shaped so as to produce an electric field which will act upon the electron beam 17 in a manner that varies with the horizontal `displacement of the electron beam relative to the center of the anode. This is done by varying the length of the anode along its width, which changes the length of time the anode interacts with each electron in the beam as the beam sweeps by. Ideally, the length of the anode in the direction of the electron beam would equal sin 21rWd/21rWd, where d is the horizontal distance from the center of the anode, and 1/azW is the total distance between adjacent anodes. This configuration is impossible to implement, and therefore another function, namely, length equals eXp(l6W2d2) over the interval d 1/2 W, is used. This substitution causes a deviation from the desired deflection pattern which results in some distortion in the final oscilloscope trace. This distortion increases with the frequency of the input signal, and hence limits the frequency response of the system. It is recognized that other anode configurations might be employed here, producing different distortions.

In operation, referring to FIGURE 3, the input signal whose waveform is to be displayed is fed into the input terminals 11 and 12. At any desired time, the pulse generator 13 is caused to pulse, initiating the action whereby the input signal is sampled. The input signal source is removed, and, referring to FIGURE 5, the electron beam 17 is caused to sweep horizontally Iby applying externallylproduced signals to the horizontal deflection plates 19. As the sweep progresses the electron beam is vertically deflected by the electric potentials on the anodes. As the electron beam traverses the fluorescent screen 20, it produces a trace proportional to the waveform of the input signal plus a fixed bias.

What is claimed is:

1. An electrical device for deflecting the electron beam in a cathode ray tube by an electrical signal comprising:

(a) a transmission line, situated in a cathode ray tube at right angles to the electron beam, having a heated common conductor treated so as to act as a cathode, and having spaced along its length and adjacent to the said common conductor, between the said common conductor and the center conductor of the said transmission line, a series of electrodes, each electrode forming the anode of a distinct diode having the said common conductor as its cathode, the said electrodes acting as electrostatic deflection plates and being so oriented that the said electron beam comes in proximity to and is deflected by each electrode in turn as the electron beam is caused to sweep, each electrode being in a configuration such that the resulting deflection of the said electron beam varies in a pre-selected pattern as the electron beam sweeps by, said pattern being selected to approximate a sin 21rWd/211-Wd function, where d is the displacement of the said electron beam from the center of the said electrode, and 1/QzW is the distance between centers of adjacent electrodes;

(b) a means for applying an electrical signal to one end of the said transmission line;

(c) a means for biasing the said diodes in their reverse direction;

(d) a pulse generator which momentarily overcomes the reverse bias of each said diode, causing the diode to momentarily conduct, thereby accumulating on the anode of each said diode an electric charge which varies with the electric potential on the said transmission line at the location of the said diode at the instant the diode is caused to conduct.

2. An electrical device for deflecting the electron beam in a cathode ray tube by an electrical signal according to claim 1, characterized further by the said pulse generator being connected to the end of the said transmission line opposite to that end to which the said electrical signal is applied, said pulse generator causing a pulse to travel down the transmission line in a direction opposite to that of the said electrical signal.

3. An electrical device comprising:

(a) means including a transmission line to simultaneously obtain a plurality of substantially instantaneous amplitude samples, in the form of electric charges on a series of distinct electrodes, of a time-varying electrical function,

(b) the said distinct electrodes, each electrode to store one of the said amplitude samples, and each electrode also to deflect by virtue 'of its stored electrical charge the electron beam in a cathode ray tube, and hence the trace on the screen of the said cathode ray tube, an amount depending on the quantity of the said electrical charge, as the said electron beam is caused to sweep by the said electrode.

4. An electrical device for deflecting the electron beam in a cathode ray tube by an electrical signal comprising:

(a) a transmission line, having spaced along its length and between its center conductor and its common conductor a series of electrodes, each electrode forming the anode of a distinct diode, the cathode of each `said diode being formed by a portion of the said common conductor, each said electrode to deflect the electron beam in a cathode ray tube by an amount proportional to the electric charge on the electrode as the electron beam is caused to sweep by the electrode;

(b) a means for applying an electrical signal to one end of t-he said transmission line;

(c) a means for biasing the said diodes in their reverse direction;

(d) a pulse generator which momentarily overcomes the reverse bias of each said diode, causing the diode to momentarily conduct, thereby accumulating on the anode of the diode an electric charge which varies with the electric potential 'on the said transmission line at the location of the said diode at the instant the diode is caused to conduct.

5. An electrical device for deflecting the electron beam in a cathode ray tube by an electrical signal according according to claim 4, characterized further by each said electrode being in a configuration such that the resulting deflection of the said electr-on beam varies in a pre-selected pattern as the electron beam sweeps by, said pattern being selected to approximate a sin 21rWd/21rWd function, where d is the displacement of the said electron beam from the center 'of the said electrode, and 1/zW is the distance between centers of adjacent electrodes.

References Cited UNITED STATES PATENTS 2,920,231 l/ 1960 Beurrier 315-30 2,921,227 l/1960 MacKay 313-78 X 2,955,231 10/1960 Aiken 315-169 JOHN W. CALDWELL, Primary Examiner.

T. A. GALLAGHER, R. L. RICHARDSON,

Assistant Examiners. 

3. AN ELECTRICAL DEVICE COMPRISING: (A) MEANS INCLUDING A TRANSMISSION LINE TO SIMULTANEOUSLY OBTAIN A PLURALITY OF SUBSTANTIALLY INSTANTANEOUSE AMPLITUDE SAMPLES, IN THE FORM OF ELECTRIC CHARGES ON A SERIES OF DISTINCT ELECTRODES, OF A TIME-VARYING ELECTRICAL FUNCTION, (B) THE SAID DISTINCT ELECTRODES, EACH ELECTRODE TO STORE ONE OF THE SAID AMPLITUDE SAMPLES, AND EACH ELECTRODE ALSO TO DEFLECT BY VIRTUE OF ITS STORED ELECTRICAL CHARGE THE ELECTRON BEAM IN A CATHODE RAY TUBE, AND HENCE THE TRACE ON THE SCREEN OF THE SAID CATHODE RAY TUBE, AN AMOUNT DEPENDING ON THE QUANTITY OF THE SAID ELECTRICAL CHARGE, AS THE SAID ELECTRON BEAM IS CAUSED TO SWEEP BY THE SAID ELECTRODE. 